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- Biaxial fiber orientation (1)
- Dielectric analysis (1)
- Dielektrizitätszahl (1)
- Elektrisches Kabel (1)
- Epoxide (1)
- Faserorientierung (1)
- Flachs (1)
- Flax/epoxy composites (1)
- Hochfrequenz (1)
- Koaxialkabel (1)
- Microstructure flax/epoxy (1)
- RF attenuation (1)
- Rauigkeit (1)
- Relative permittivity (1)
- Unidirectional fiber orientation (1)
- Verbundwerkstoff (1)
- Verdrillung <Elektrotechnik> (1)
- Verschleißprüfung (1)
- coaxial (1)
- surface roughness (1)
- transmission phase (1)
- twisted-pair (1)
- wear-level monitoring (1)
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- FB Technik (2)
Dielectric properties of unidirectional and biaxial flax/epoxy composites at frequencies up to 1 GHz
(2023)
The relative permittivity of flax/epoxy composites in unidirectional and biaxial orientations was mapped in the frequency range of 1 kHz to 200 kHz, and for the first time in the range of 1 MHz to 1 GHz. In addition, permittivity was investigated for the first time in the temperature range between − 20 °C and 50 °C. These composites, produced using the vacuum infusion process, are increasingly used for sustainable and lightweight structural components in the automotive industry. The relative permittivity was determined using a self-developed plate capacitor with an LCR bridge and an impedance analyzer. An examination of the microstructure of the flax/epoxy composites shows that the fibers are disordered in the composite, resulting in local variations in fiber volume fraction. Furthermore, it was shown that the matrix also infiltrates into the fiber itself, resulting in an increase of the matrix fraction. It was found that unidirectional fabrics had a higher relative permittivity than biaxial fabrics, due to a higher fiber volume fraction and lower proportion of epoxy. The results suggest that it is the fiber volume fraction, rather than the manufacturing process and fiber orientation, that primarily determines the relative permittivity. It was also found that the permittivity continues to decrease below room temperature and thus behaves in a manner typical of the material in this temperature range as well.
In this paper, the radio frequency (RF) behavior of mechanically stressed coaxial and for the first time also twisted-pair transmission lines is investigated over their service life. The main goal is to enable predictive maintenance for cables in moving applications and avoid preventive replacement. This also reduces the use of high-cost resources. For this purpose, stranded and solid-core variants of coaxial and twisted-pair type cables are mechanically loaded on the two-pulley apparatus according to EN 50396. Their RF transmission (S21) behavior is measured using a vector network analyzer and presented over bending cycles. For the first time, the phase response of mechanically loaded transmission lines is evaluated with respect to their service life. Two significant causes for the increasing attenuation and altered phase response are identified: breakage in foil screen and increasing surface roughness on the copper conductors. The identified causes are supported with literature evidence. Through measurements and theoretical calculations, it is proven that the phase is much more suitable for an assessment of the remaining service life than the amplitude. The findings can be used to implement a cable monitoring system in industrial environments which monitors the lines in-situ and reminds the user to replace them, whenever a certain wear-level is reached.